noun
voucher; coupon; supplementary ticket
A ticket or coupon that provides a discount, free service, or additional benefit, often issued alongside a main ticket or as part of a promotion.
この補助券で入場料が半額になります。
This voucher gives you half off the admission fee.
補助券を提示すると、ドリンクが一杯無料です。
Show this coupon and get one free drink.
割引券 is a discount ticket, focusing on price reduction, whereas 補助券 may offer free items or services in addition to discounts.
Compound of 補助 (ほじょ, 'assistance, support') and 券 (けん, 'ticket, coupon').